Three types of sprinkler heads are known in the art, a "frame yoke" type which has a deflector disposed at the tip of a frame in a horseshoe configuration; an "embedded" type which has a deflector adapted to be lowered a predetermined distance from within a frame when fire occurs; and a type in which a plurality of holes or slits are provided in a deflector.
The sprinkler head of the frame yoke type significantly protrudes from a surface of ceiling, so that it is not satisfactory in an esthetic sense. Further, it is easily damaged by an object impacting against the sprinkler head after installation onto the ceiling. The sprinkler heads of the embedded type and the type which has a plurality of holes or slits in the deflector, on the other hand, do not significantly protrude from the surface of ceiling, so that they are satisfactory in an esthetic sense. Furthermore, they are not easily damaged by an impact of an object.
It should be noted, however, that the sprinkler heads of a embedded type and the type which has a plurality of holes or slits in the deflector have disadvantages in that a thermosensitive part thereof tends to be broken easily if external force or shock is given thereto, since such thermosensitive part is located at a lower part of the sprinkler head. On the other hand, the thermosensitive part of the sprinkler head of the frame-yoke type is enclosed within a frame, so that it may be kept undamaged even if external force or shock is given to the sprinkler head.
An example of prior art sprinkler heads of the embedded type is shown in FIGS. 4 and 5, for the purpose of illustrating its construction.
A sprinkler head of the embedded type includes a main body 1, a frame 2, a valve 3, a deflector 4, and a thermosensitive part 5.
The main body 1 includes a central bore 6 for introducing water therein. A lower portion of the main body 1 constitutes a valve seat 7. An upper portion of the main body 1 includes a male-threaded portion 8 formed in the outer periphery thereof. The lower end of the main body 1 constitutes a flange 9.
The frame 2 is of a cylindrical configuration. The lower end of the frame 2 constitutes an inner flange 10. The upper end of the frame 2 is threadingly engaged with the flange 9 of the main body 1.
The valve 3 is sealingly engaged with the valve seat 7 of the main body. A deflector 4 is positioned below the valve 3. The valve 3 is supported by the thermosensitive part 5 through a guide post 11.
The thermosensitive part is disposed at a lower part of the sprinkler head. Construction of such a thermosensitive part is well known in the art (see Japanese patent Publication No. 58-36985, for example), and hence it is believed no further explanation thereof necessary. A heat collection plate 12 is attached to the lower end of the thermosensitive part 5. It is to be noted that a heat collection plate attached to prior art sprinkler heads is constituted by a member of simple cup-shaped configuration.
It should be understood that the thermosensitive part 5, which may detect occurrence of fire and or destroy itself in response thereto, is the most important part of the sprinkler head. This is because that the thermosensitive part 5 should be assembled or destroyed in a predetermined period of time in response to a temperature ranging from 72 to 96 degrees Celsius upon occurrence of fire, while, during normal state, i.e., occurrence of no fire, it should support the valve sealingly engaged with the valve seat of the sprinkler head so as to prevent any leakage of extinguishing agent therethrough.
It should be noted, however, that, when external force or shock is given to the thermosensitive part, displacement or misalignment between several parts constituting the thermosensitive part occurs. Thus, when such a damaged sprinkler head, which has been connected to a piping within a ceiling, is pressurized by extinguishing agent introduced thereinto from the piping, may be erroneously actuated or disassembled, notwithstanding that no fire occurs in reality. Apart from such an erroneous actuation, such a damaged sprinkler head tends to permit leakage of extinguishing agent due to the fact that the valve is disengaged from the valve seat, thus causing office automation equipment or furniture, which is rather expensive, to be wetted by extinguishing agent.
If it is possible to visually recognize the fact that the thermosensitive part has been damaged, a sprinkler head having such a damaged part may be replaced in order to prevent the sprinkler head from causing erroneous actuation or leakage (collectively referred to as "erroneous actuation" hereinbelow). Conventional sprinkler heads include, however, a heat collection plate disposed below the thermosensitive part which is relatively rigid. Thus, such a heat collective plate deforms slightly when a shock or external force is applied thereto. Such a slight deformation is not easily recognized. Accordingly, such a damaged sprinkler head is usually installed onto a ceiling since no remarkable change could be recognized visually, whereby erroneous actuation of the sprinkler may be caused afterward.